The present invention relates to fiber optic probes for use in making on-wafer measurements of the parameters of photodetectors and other optoelectronic devices.
An existing fiber optic probe for use in making measurements is shown in Modolo et al., “Wafer Level High-Frequency Measurements of Photodetector Characteristics,” Applied Optics, volume 27, pages 3059-3061 (1988). In the Modolo et al. probe, an optical fiber is pressure fitted into the grooved periphery of a disc segment mounted on a probe arm so that the fiber extends longitudinally through a bend of 90 degrees around the disc segment and thence to a pulsed optical signal source. To probe a given device, the probing end of the optical fiber is advanced longitudinally toward the surface of the test device until it is approximately 100 micrometers from the surface of the device.
One of the limitations of the Modolo et al. probe is that the optical fiber is pressure fitted into the peripheral groove of the disc segment and therefore cannot move longitudinally relative to the disc segment. Thus, as the probing end of the optical fiber is moved longitudinally toward the surface of the test device, any slight over travel of movement will cause the end of the fiber to impact against the surface causing possible damage either to the surface of the test device or to the end of the fiber, or both.
Rumbaugh, U.S. Pat. No. 5,101,453, discloses a fiber optic wafer probe that includes a probe body along which an optical fiber extends to protrude from the tip of the probe body. The probe body loosely guides the optical fiber so that at least a significant portion of the length of the optical fiber is movable longitudinally with respect to the tip and probe body. The purpose of the movability of the optical fiber is to enable the optical fiber to buckle longitudinally in response to longitudinal over-travel of the fiber toward the test device. After repeated use, the optical fiber is replaced by a new optical fiber and connector. Unfortunately, replacement of the optical fiber insert is both expensive and time consuming. Further, the angle of incidence provided by the optical probe may be unsuitable for a particular probe station or probing requirements. Moreover, the bulky nature of the optical probe make it unsuitable for environments with limited available space.
Clyne, U.S. Pat. No. 6,071,009, discloses a tubular arrangement with a fiber optic lead contained therein specifically designed for measuring the surface temperature of wire-bonded semiconductors and the like. A temperature sensor is attached to the end of the fiber optic lead to facilitate temperature measurements. However, the design disclosed by Clyne is specifically designed for surface temperature measurements and is generally ineffective for optical probing of semiconductor wafers.